1. Field of the Invention
The present invention relates generally to building components and more particularly to an apparatus for supporting a concrete floor and composite floor systems constructed therewith.
2. Discussion of the Prior Art
Many commercial buildings and some larger, multi-story residential complexes, such as apartment buildings or condominiums, utilize concrete floor decking or concrete floors in their construction. Concrete floor decking has also become increasingly popular in residential and smaller constructions over the last decade. Concrete floor support systems have several advantages over traditional decking materials, such as strength, rigidity, durability, mold resistance, sound attenuation, suitability for in-floor radiant heating and the availability of decorative concrete finishes.
Traditional concrete flooring systems were adapted from commercial construction, and generally constructed by spanning steel or wood joists between structural walls or primary structural members, spacing or bridging the joists with rebar or blocking members to provide lateral support to the joists, and laying plywood, steel, aluminum, or fiberglass decking on or between the joists and pouring a thick concrete layer over the decking. The resulting flooring systems are heavy and require significant time to install. Further, in order to bear the additional weight of the decking and concrete layer during curing, the decking panels must be shored (or braced), adding to the cost of the systems. In smaller constructions, such as residential applications, these traditional systems were generally too expensive and logistically challenging to install.
Further, in application, conventional concrete flooring systems are subject to significant horizontal and vertical forces, and in particular, horizontal shear occurring along the longitudinal top of primary and secondary joist members. Indeed, these systems ultimately fail because of loss of interfacial force in the shear span.
Composite concrete floor support systems offer a solution to traditional concrete floor systems. Composite systems utilize steel joists having a top chord or portion that is embedded into the poured concrete deck. The top chord then forms a shear connector to prevent slippage from occurring between the concrete slab and the joist, due to horizontal shear along the joist, which can reduce the amount of reinforcement required over the traditional systems.
Various forms of shear connectors have been developed, including elongated studs welded to the top chord of the joist member. The studs are embedded in the concrete, thereby transferring horizontal shear forces from the slab to the beam. However, these studs are welded to the joist after the joist has been connected to the structure during erection, requiring significant labor and time, and they can be hazardous to crew members after installation, but before the concrete has been poured. Other types of shear connectors include, joists having an irregular or S-shaped tap chord, such as the Hambro™ joist, or alternatively, a shear connector of the type disclosed in U.S. Pat. No. 7,013,613 to Boellner et al., which teaches an extended length shear connector including protrusions and indentations on the surface thereof.
Regardless of the shear connector used in the prior art systems described above, these systems still require reinforcement of the concrete layer. In particular, rebar (reinforcing bar), metal mesh, decking or cross braces are placed over or in between the joists to reinforce the concrete layer before the concrete is poured. Accordingly, this type of composite system, while having increased strength over non-composite systems, can be heavy and expensive due to the added cost of reinforcement material. However, rebar and other metal reinforcements are subject to corrosion and deterioration of the floor. Further, in systems where the reinforcement is positioned on top of the top chord or shear connector, these systems are subject to failure due to tearing of the deck near the shear connector.
In addition, many of the prior art systems require removable framing systems to be in place before construction and removed after the concrete has cured, adding to the cost of installation of these types of composite systems.
Accordingly, there is a need for a lighter floor support system for use with concrete floor decking, in particular, for use in above-grade and residential constructions, while also offering decreased costs and ease of installation on-site.